Why Soundwave was left out of the 2007 Transformers movie

Soundwave finally appears in "Revenge of the Fallen", the sequel to "Transformers" and the last written by Orci and Kurtzman. In this film, Soundwave (voiced again by Welker) transforms into a satellite, remaining in Earth's orbit and monitoring communications. For the first part of the film, he puppeteers the rebirth of Megatron. His connection to Ravage is also reinvented; the Decepticon Panther transforms into a missile that Soundwave can fire through the atmosphere to the Earth's surface.

In the third film, "Dark Side of the Moon", Soundwave has arrived on Earth and is now transformed into a brand new Mercedes-Benz. In keeping with his role as spymaster, he poses as the new car belonging to Sam's girlfriend Carly (Rosie Huntington-Whiteley) and has Laserbeak (Keith Szarabajka) act as his killer. He meets an abrupt end in the third act, but the prequel/reboot "Bumblebee" brings him back and makes him the same as his classic self. Despite the cassette-player style of Soundwave's appearance, the film sidesteps the size-shifting issue by never showing him transforming.

2010's "Transformers: Prime" cartoon (developed in part by Orci and Kurtzman) presents, for my money, Soundwave's best modern update. He transformed into a Predator drone plane and so his robot mode was not square, but thin and pointed (the drone's wings formed his arms, see here). His face was also a blank screen, taking his classic visor to the next extreme. "Prime" Soundwave was not only taciturn, but completely silent; when he chose to communicate verbally, it was through recordings of other characters (more than once, Soundwave literally threw Starscream's words in his face). This also makes Soundwave even scarier; the implication is that he always listens.

If Orci and Kurtzman had come up with the idea earlier, I think "Prime" Soundwave might have been the perfect template to bring the character into live-action.